Microsoft Ultimate Word Games

The description is worded very strangely for some reason. You have to correctly finish a 10-letter answer, not a clue.

This achievement is unavoidable while working up to level 80, as a good deal of puzzles have 10+ letter words. Many 10x10 and 15x15 grids have entries that span the whole puzzle. You can use hints if you need them, just as long as you have the correct answer entered when you check the puzzle or the word. Once a 10+ letter answer is green from being checked correctly, the achievement will unlock.